The present invention relates to a tool for drilling an orifice, the tool being of the type comprising:
a cutter support designed to be rotated about a first axis of rotation that is to coincide with the axis of the orifice; and
a cutter rotatably mounted on the cutter support and having a central axis forming a second axis of rotation parallel to the first axis of rotation and spaced apart therefrom by a non-zero offset, the cutter being designed to be rotated about the second axis of rotation relative to the cutter support in order to drill the orifice.
The invention applies in particular to drilling tools used in the aviation industry.
A tool of the above-specified type makes use of an xe2x80x9corbitalxe2x80x9d drilling method, where xe2x80x9corbitalxe2x80x9d refers to the motion of the cutter about the first axis of rotation.
Compared with a conventional tool in which the cutting head is a drill bit on the axis of the orifice to be drilled, such an orbital tool makes it possible to reduce both the rotary driving torque needed for the cutting head and also the axial penetration force needed for enabling the cutting head to penetrate into the workpiece being drilled.
Nevertheless, in a tool of the above-specified type, the cutter extends generally axially from outside the workpiece to be drilled into the inside of the orifice. Furthermore, the radial extent of the cutter support relative to the first axis of rotation is greater than the radius of the orifice drilled in the workpiece. While drilling is taking place, the cutter is thus cantilevered out and is subjected to high bending forces which can harm, in particular, the shape and the precision of the orifices that are obtained.
Thus, tools of the above-specified type are poorly adapted to making orifices having a large length/diameter ratio.
An object of the invention is to solve that problem by providing a tool of the above-specified type which makes it possible to make orifices having a large length/diameter ratio.
To this end, the invention provides a tool of the above-specified type, wherein at least a front segment of the cutter support has a maximum radial extent relative to the first axis of rotation that is less than or equal to the radius of the orifice so as to enable the front segment of the cutter support to penetrate into the orifice during drilling.
In particular embodiments of the invention, the tool may comprise one or more of the following characteristics taken singly or in any technically feasible combination:
the maximum radial extent of the front segment of the cutter support is substantially equal to the radius of the orifice so that the front segment of the cutter support possesses at least one bearing surface for bearing against the wall of the orifice to guide the cutter during drilling;
bearing surface of the cutter support has an outline that is circular or in the form of an arc of a circle centered on the first axis of rotation and with a radius that is substantially equal to the radius of the orifice;
the cutter support comprises a tube;
the tool includes swarf-removal means for removing swarf formed by the cutter;
the swarf-removal means comprise an opening passing radially through the tube;
the tool includes an intermediate member for transmitting rotary motion to the cutter, and at least one segment of the intermediate member is both centered on the first axis of rotation and rotatable about the first axis of rotation; and
the cutter support is centered on the first axis of rotation.
The invention also provides a machine for drilling an orifice, the machine comprising:
a drilling tool as defined above; and
motorized drive means for driving the cutter support in rotation about the first axis of rotation and for driving the cutter in rotation about the second axis of rotation.
In a variant, the machine includes a spindle on which the cutter support is removably mounted, the spindle being rotatable about the first axis of rotation by the drive means.
The invention also provides a method of drilling an orifice in a workpiece, the method comprising the steps of:
driving the cutter support of a drilling tool as defined above in rotation about a first axis of rotation;
driving the cutter in rotation about the second axis of rotation;
pressing the cutter axially forward against the part in order to drill the orifice therein; and
causing at least the front segment of the cutter support to penetrate into the orifice as it is being drilled.